This invention relates to echogenic coatings for medical devices used with ultrasound imaging systems and, more particularly, to echogenic coatings that also afford electrical insulative protection.
Ultrasound imaging is widely used in medical applications to noninvasively observe structures within the human body, such as, for example, cardiac structures, the vascular system, the fetus, the uterus, the abdominal organs and the eye. In addition to imaging physiological structures and tissue, ultrasound imaging has also been employed to image medical devices that are inserted into tissue or passageways of the patient. In a typical imaging system, short bursts of ultrasound energy are directed into a patient""s body with a transducer. The returning reflected ultrasound energy, or echoes, are received by the same transducer and are converted to electrical signals. The signals representing the reflected energy are processed and formatted into a video image of a target region.
A variety of approaches have been used to enhance ultrasonic images. For example, U.S. Pat. No. 5,201,314 describes a medical device that is insertable into tissue or a passageway and imageable with sonic imaging equipment. The device includes an elongated insertable member that has an interface having a shape that is responsive to the sonic beam for producing the image. The elongated member includes a substance such as spherically or other geometrically-shaped particles that have a predetermined contour for establishing the interface. This contoured substance is contained within the material of the elongated member or alternatively or in combination attached to or embedded in the outside surface of the member material. In one case, the member material comprises a plastic for surrounding spherically-shaped glass particles, which may consist of a high density metal such as barium or tungsten or a glass material.
U.S. Pat. No. 5,921,933 describes medical devices that are employed within the human body and which purportedly have enhanced ultrasound visibility by virtue of incorporation of an echogenic material on the device surface. The material is fabricated by incorporating particles of sonically reflective materials, for example, iron oxide, titanium oxide or zinc oxide into a biocompatible plastic. The echogenic material can be fabricated by mixing the reflective particles with a powdered thermoplastic or thermosetting material such as a polyether amide, a polyurethane or an epoxy, or polyvinylchloride followed by thermal processing of the mixture to provide a material of increased sonic reflectance which may be applied as a coating on the devices.
U.S. Pat. No. 5,081,997 describes medical devices that include an echogenic body member that is at least partially made up of a composite material which is echogenically imageable in the patient. The composite material includes a plastic matrix material with discrete sound reflective particle embedded therein. Examples of suitable plastics include urethane, silicone, polyethylene, polytetrafluorethylene. The reflective particles are made of a hard material, such as glass particles.
While prior art medical devices having echogenic materials coated thereon can improved ultrasonic imaging, conventional echogenic materials are not suitable for use with medical devices that are exposed to high voltage electrical energy, e.g., radio frequency (RF) energy. The art is in search of echogenic materials that also afford adequate electrical insulation.
The present invention is based in part on the discovery that metal substrates that are coated with an echogenic material comprising an electrically insulative base layer and an echogenic layer demonstrate both improved ultrasonic imaging and protection against RF electrical breakdown. The echogenic material is particularly suited for coating a medical device component which is viewed along its length.
In one aspect, the invention is directed to an echogenic material that includes:
an electrically insulative base layer and
an echogenic layer that comprises a polymeric matrix that (i) defines a plurality of void spaces, (ii) includes glass microsphere particles, or (iii) both defines a plurality of void spaces and includes glass microsphere particles, wherein the echogenic layer is formed on the base layer.
In another aspect, the invention is directed to a process for forming an echogenic layer on a substrate surface that includes the steps of:
(a) applying an electrically insulative base layer on the substrate surface; and
(b) creating an echogenic layer on the insulative base layer wherein the echogenic layer comprises a polymeric matrix that (i) defines a plurality of void spaces, (ii) includes glass microsphere particles, or (iii) both defines a plurality of void spaces and includes glass microsphere particles, wherein the echogenic layer is formed on the base layer.
Preferred techniques for fabricating the echogenic layer are electrostatic spraying and fluidized bed coating.
In a further aspect, the invention is directed to a system for applying RF energy to tissue that includes:
an ultrasonic transducer means for sensing a location in the tissue to be treated; and
means for applying RF energy that includes an RF probe having a distal end and an RF electrode mounted on the RF probe distal end wherein the RF probe has a surface that has an echogenic material coated thereon which comprises an electrically insulative base layer and an echogenic layer.
Preferably, the echogenic layer includes a polymeric matrix that (i) defines a plurality of void spaces, (ii) includes glass microsphere particles, or (iii) both defines a plurality of void spaces and includes glass microsphere particles.
In yet another aspect, the invention is directed to a medical device for insertion into biological tissue having an echogenic portion of enhanced visibility in an ultrasound scan, wherein the echogenic portion includes a coating comprising an echogenic layer and an electrically insulative layer.
In still another aspect, the invention is directed to a medical device for insertion into biological tissue having a shaft member and a source of RF energy wherein the shaft member has an outer surface that is coated with a coating that includes an echogenic layer and an electrically insulative layer.
In another further aspect, the invention is directed to a method for sonically imaging an echogenic medical device in biological tissue, that includes:
selecting a medical device that includes:
(i) an ultrasonic transducer means for sensing a location in the tissue to be treated; and
(ii) means for applying RF energy that includes a shaft member having a distal end and an RF electrode mounted on the shaft member distal end wherein the shaft member has an echogenic material coated thereon which comprises an electrically insulative base layer and an echogenic layer;
inserting the shaft member into the tissue;
directing a sonic beam towards the shaft member;
receiving an image of the shaft member;
maneuvering the RF electrode to the location in the tissue to be treated; and
applying RF energy to the tissue.
In another further aspect, the invention is directed to a method for manufacturing an echogenic medical device for insertion into biological tissue and imageable with sonic imaging equipment, that includes:
providing a medical device that includes means for applying RF energy that includes a shaft member having a distal end and an RF electrode mounted on the shaft member distal end; and
applying an echogenic coating on the shaft member wherein the echogenic coating comprises an electrically insulative base layer and an echogenic layer.